This invention relates to a fire sensor device for detecting both flames and smoke produced by a fire.
Conventional fire sensor devices which are generally used include a heat sensor, which utilizes the heat generated by a fire, and a smoke sensor which catches smoke. Known heat sensors include, for example, bimetal types of heat sensor, thermal semiconductor types of heat sensor, and thermocouple types of heat sensor. A bimetal type of heat sensor consists of a metal of a low coefficient of expansion and a metal of a higher coefficient of expansion attached to each other. When this bimetal strip which is fixed at one end is heated, it bends toward the metal of the lower coefficient of expansion. This heat sensor uses metals which are displaced in proportion to the temperature applied thereto. Thermal semiconductor and thermocouple heat sensors utilize the Seebeck effect. Smoke sensors include, for example, photoelectric smoke sensors which utilize dimmed or scattered light to detect smoke. A dimmed-light type of smoke sensor utilizes a property such that light is attenuated by smoke, and is actuated when the density of the smoke in a smokedetecting portion of the sensor has reached a predetermined level. FIG. 1 shows a dimmed-light type of fire sensor in which the light radiated from a light source 2 in a light-emitting unit 1 is turned into parallel rays of light 2' by a lens 3, the rays of light 2' reach a lens 6 in a light-receiving unit 5 positioned opposite to the light-emitting unit 1. When smoke flows into the region (optical path) between the lenses 3, 6 through which the parallel rays of light pass, the quantity of light received by a light-receiving element 7 decreases to an extent that is proportional to the flow rate of the smoke. When the quantity of light received by the element 7 reaches a predetermined level, an output 8 is obtained, i.e. the sensor starts to operate. Reference numeral 4 denotes a light-receiving element in the light-emitting unit 1. This element 4 is used to compensate for changes in brightness, e.g. when the luminance of the light source drops.
The use of these two types of devices, a heat sensor and a smoke sensor, is permitted under the Fire Services Act. However, all the various kinds and magnitudes of fires cannot be dealt with in practice with these two sensors along. In order to discover a fire early, the detection of flames is necessary in some cases. A known flame sensor includes an infrared sensor and an ultraviolet sensor. The infrared sensor picks up the electromagnetic radiation emitted by the flames of a fire, and is capable of detecting the distinctive radiation of a wavelength in the vicinity of 4.3 .mu.m of the high-temperature CO.sub.2 gas generated when a combustible material, such as town gas, gasoline or wood, burns. However, an infrared sensor is expensive and is likely to be affected by sunlight and electric light, it is also not able to detect smoke.